Coordination Polymers from Biphenyl-Dicarboxylate Linkers: Synthesis, Structural Diversity, Interpenetration, and Catalytic Properties

The present work explores two biphenyl-dicarboxylate linkers, 3,3′-dihydroxy-(1,1′-biphenyl)-4,4′-dicarboxylic (H4L1) and 4,4′-dihydroxy-(1,1′-biphenyl)-3,3′-dicarboxylic (H4L2) acids, in hydrothermal generation of nine new compounds formulated as [Co2(μ2-H2L1)2(phen)2(H2O)4] (1), [Mn2(μ4-H2L1)2(phen)2]n·4nH2O (2), [Zn(μ2-H2L1)(2,2′-bipy)(H2O)]n (3), [Cd(μ2-H2L1) (2,2′-bipy)(H2O)]n (4), [Mn2(μ2-H2L1)(μ4-H2L1)(μ2-4,4′-bipy)2]n·4nH2O (5), [Zn(μ2-H2L1)(μ2-4,4′-bipy)]n (6), [Zn(μ2-H2L2)(phen)]n (7), [Cd(μ3-H2L2)(phen)]n (8), and [Cu(μ2-H2L2) (μ2-4,4′-bipy)(H2O)]n (9). These coordination polymers (CPs) were generated by reacting a metal(II) chloride, a H4L1 or H4L2 linker, and a crystallization mediator such as 2,2′-bipy (2,2′-bipyridine), 4,4′-bipy (4,4′-bipyridine), or phen (1,10-phenanthroline). The structural types of 1–9 range from molecular dimers (1) to one-dimensional (3, 4, 7) and two-dimensional (8, 9) CPs as well as three-dimensional metal–organic frameworks (2, 5, 6). Their structural, topological, and interpenetration features were underlined, including an identification of unique two- and fivefold 3D + 3D interpenetrated nets in 5 and 6. Phase purity, thermal and luminescence behavior, as well as catalytic activity of the synthesized products were investigated. Particularly, a Zn(II)-based CP 3 acts as an effective and recyclable heterogeneous catalyst for Henry reaction between a model substrate (4-nitrobenzaldehyde) and nitroethane to give β-nitro alcohol products. For this reaction, various parameters were optimized, followed by the investigation of the substrate scope. By reporting nine new compounds and their structural traits and functional properties, the present work further outspreads a family of CPs constructed from the biphenyl-dicarboxylate H4L1 and H4L2 linkers.


Figure S4
Typical 1 H NMR spectrum of the reaction mixture p. S8 Calculation of the product yield and selectivity p. S8 Figure S5 Accumulation of products vs. time p. S9 Figure S6 Catalyst recycling experiments p. S9 Figure S7 PXRD patterns for 3 p. S10

Figure S8
Proposed catalytic cycle for Henry reaction catalyzed by 3 p. S11

Table S1
Selected bond lengths and angles for compounds 1-9 p. S10
Synthesis and analytical data for 1-9.
[  Figure S1. Transmittance (%) FTIR spectra of compounds 1-9. Figure S2. PXRD patterns of compounds 1-9 at room temperature. Black patterns correspond to the experimental data obtained using the as-synthesized bulk samples. Red patterns were simulated from the single crystal X-ray data (CIF files).

S7
Luminescent Properties. The emission spectra of compounds 1-9, H 4 L 1 and H 4 L 2 were recorded in the solid state S8 at room temperature (Fig. S3). The spectra of H 4 L 1 and H 4 L 2 disclose two weak emission bands centered at 470 and 483 nm. In contrast to H 4 L 1 and H 4 L 2 , zinc(II) and cadmium(II) derivatives feature bands of a more pronounced intencity with maxima in the 440−458 nm range, namely 457 nm for 3, 440 nm for 4, 458 nm for 6, 455 nm for 7, and 445 nm for 8. These bands are associated with an intraligand π-π* or n-π* transitions of main carboxylate ligand. S1-S3 An enhanced luminescence of 3, 4, and 6-8 vs. H 4 L 1 and H 4 L 2 is likely due to the coordination of ligands to Zn(II) or Cd(II), which may strengthen the rigidity of ligands and diminish a loss of energy from radiationless decay. S3-S5 However, compounds 1, 2, 5, and 9 display very weak luminescence and almost no emission, which is probably attributed to the fluorescence quenching of Co 2+ , Mn 2+ , and Cu 2+ by the ligands present in these compounds. S6-S9 Figure S3. Solid-state emission spectra of 1-9, H 4 L 1 and H 4 L 2 at room temperature (λ ex = 316 nm). Figure S4. Typical 1 H NMR spectrum of the reaction mixture with integration of signals for determination of the Henry reaction products (conditions of Table 3, entry 7; 4-nitrobenzaldehyde substrate, catalyst 3).

S9
Calculation of the product yield and selectivity based on the data of Figure S4 Yield: Total amount of compounds: 4-nitrobenzaldehyde + anti + syn = 1.00 + 3.52 + 4.38 = 8.90.